I have never seen a silver fetish necklace. Fetish necklaces were mostly the Zuni tribe. The Zuni are close to the Mexico border so what happened a lot is that jewelers from Mexico would create pieces that stylistically reflected Native pieces. If your piece is solid silver then it has a silver value regardless of origin. a clue is usually the beads used in between the fetish animals. I would have to see the piece to give you an idea of who made it. If the animals are three dimensional that would be an odd native piece simply because the Natives believe the stone tells them what animal it should be. To have a silver cast animal takes the element of spirit out of the piece.